Field
The presently disclosed subject matter relates to a biaxial optical deflector, a radar system using the same and its manufacturing method.
Description of the Related Art
In an automobile safety system, a laser radar system is provided to detect a distance and angle between the driver's vehicle and its object or preceding vehicle. As a result, when the distance between the driver's vehicle and its preceding vehicle is smaller, the driver's vehicle is automatically decelerated for a time or a distance and, at worst, the driver's vehicle is stopped.
Such a laser radar system requires a function for scanning an object or a preceding vehicle at a wide angular view with a high angular resolution to avoid a dead space. Particularly, when the driver's vehicle is driving, the laser radar system requires a high speed scanning operation in addition to the high angular resolution. In order to provide such a high speed scanning operation and such a high angular resolution, a movable mirror such as a Galvano mirror or a polygon mirror is usually used; however, a micro electro mechanical system (MEMS) mirror (optical deflector) has recently been used.
On the other hand, in order to irradiate a preceding vehicle at a distance of 100 m ahead of the driver's vehicle with a collimated laser beam, the beam-diameter of the laser beam needs to be larger than about 2 to 3 mm, so that the size of the MEMS mirror needs to be larger. However, the larger the size of the MEMS mirror, the lower the operation speed of the MEMS mirror. Note that since the resonant frequency of the MEMS mirror for a wider angular scanning is about several hundreds of Hz, it is impossible to operate the MEMS mirror at a high scanning speed.
Also, in order to introduce a laser beam reflected from the preceding vehicle via the MEMS mirror to a photo detector, the optical source, the MEMS mirror and the preceding vehicle object and the photo detector form a coaxial optical system, to alleviate the effect of noise caused by external disturbances.
In view of the foregoing, a prior art laser radar system is constructed by a laser array light source including multiple laser light sources spaced from each other and a single MEMS mirror (see: JP 2010-151958A). In this prior art laser radar system, the laser light sources are sequentially turned on to realize a high speed scanning operation.
In the above-described prior art laser radar system, however, when the number of laser light sources is smaller, the angular view and angular resolution are limited. On the contrary, when the number of laser light sources is larger, the manufacturing cost would be increased. Also, it is difficult to continuously scan the irradiation angle of laser beam over the laser light sources, so that irradiation areas or areas scanned by the laser light sources are discrete, i.e., not continuous.